Field of the Invention
This invention is an improved high speed synthetic aperture or array radar mapping system that provides a high resolution map of the surface being illuminated, using programmable type signal processors. The system of the invention is applicable to either processing and display of the area being mapped on the aircraft or to reception and processing of the radar data at different locations. Conventional radar mapping systems, in order to process the large amount of data that is received by the radar, use patch processing in which the swath of sequential radar return data is partitioned into range subswaths and then into patches in each subswath. The system of the invention utilizes this patch processing technique, but partitions the patches of data so that they can be processed in an orderly manner with a minimum of complexity and processor loading.
Description of Related Art
Prior to this invention, high speed synthetic aperture radar processing systems performed intrapulse and interpulse processing to produce two-dimensional maps by either using path processing in which the patches of data were not aligned in range or by using polar format processing, both of which require excessive digital bookkeeping of parameters and considerable loading of the processors. The intrapulse processing consists of range dechirping the received data and segregating the data in range as a function of frequency. This range segregation includes a coarse segregation to form a plurality of range subswaths from the swath or area being mapped. A final compression in range then produces range strips of the desired resolution. The interpulse processing includes azimuth dechirping of the received data as a function of aircraft motion and geometry and then segregating of the azimuth data into patches of data for each subswath. This azimuth segregation usually includes the steps of first forming a coarse division or patches in azimuth or cross range followed by forming the final resolution cells or pixels for the display map. In order to maintain a constant interpulse data rate for each subswath so that the interpulse processing will not be excessively complex, the FFT (Fast Fourier Transform) filters for providing patch filtering are equally spaced in frequency for all of the range subswaths. The cross range spacing of the adjacent filter passbands or the azimuth distance on the mapped surface reflecting data that each filter responds to its proportional to range and thus is different at each subswath. The cross range passband width of the filters on the surface increases from near range to far range of the swath being mapped. Thus, a patch area in the center of a patch filter in a near range subswath is often not in the center of a patch filter at a far range subswath. The data is partitioned in cross range but the patch filters in different range subswaths are not aligned in cross range, resulting in increased addressing and address storage of the patches of data in the processing stages.
In order to simplify processing, it would be highly desirable if a system provided equal cross range spacing between patches in all subswaths and the patches of data were aligned across subswaths in columns of constant cross range on the surface being mapped. Also, it would be advantageous if the data rate of the processing steps were reduced to provide minimum processor loading.